ACRS Humanes 2013

Transcript

1. Effects of turbidity and sedimentation on the survival of Pocillopora damicornis recruits Adriana Humanes, Katharina Fabricius, Bette Willis, Andrew Negri
2. Introduction Buddemeier et al. 2004, Hutchings & Haynes 2005, Hutchings et al.2005, Hoegh-Gulberg et al. 2007 Stressors on coral reefs
3. Runoff and coral reefs: Introduction Sediments and nutrient input in the Great Barrier Reef Lagoon have increased since 1823: Sediment - x 5.5 Nitrogen- x 5.7 Phosphorus - x 8.9 Kroon et al. 2012 Mitchell et al. 1997, 2001, Tilman et al. 2001, Smith et al. 2003, Devlin & Brodie 2005, Fabricius 2011
4. Sediments and early life histories of corals Fine sediments will stay suspended and… Introduction Organic Carbon, Nitrogen Phosphorous
5. Sediments and early life histories of corals Fine sediments will stay suspended and… Introduction Residence time of fine sediments, N and P: years to decades in the GBR lagoon All coral life history stages submitted to enriched sediments Kroon et al. 2012, Fabricius et al. 2013, Brodie et al. 2013
6. Smothered Sed Fabricius et al. 2003 Control Nut Sed + Nut Mortality (%) Introduction Coral spat survivorship under sediment stress: Tolerance to sediments At least 1 order of magnitude lower Fabricius 2005
7. Objective To measure the survivorship of β-Pocillopora damicornis recruits exposed to 1) three turbidity levels for 31 days. 2) sedimentation at several levels of organic enrichment.
8. Experiment 1: Effects of suspended sediments on recruit survivorship Sediments collected in Orpheus and sieved ˂63 µm 2 weeks 0 mg/l 124 30 mg/l 110 100 mg/l 111
9. Water sample analysis: • Total suspended solids Data analysis: SDR: Anova SAR: Kruskal-Wallis Recruit’s size and # polyps: Kruskal-Wallis Survivorship: Kaplan-Meir Data Size: Maximum diameter # of polyps Survivorship rate: % recruits alive after 31 days • Sedimentation deposition rates (SDR) • Sediment attachment rate (SAR) • Nitrogen, Phosphorus and Carbon • Pigments • Bacterial community (454 sequencing) Experiment 1: Effects of suspended sediments on recruit survivorship
10. N.S. Number of polyps/recruit p<0.05 Recruits size (mm) 0.9 1 1.1 1.2 1.3 * Experiment 1: Effects of suspended sediments on recruit survivorship • Turbidity reduces energy for growth • Clearing sediments is energetically costly (mucus production: 2.5 x more expensive than other physiological functions; Riegl & Branch 1995) • Trade-off between growth and maintenance Recruits size
11. Experiment 1: Effects of suspended sediments on recruit survivorship p<0.05 Differences after 18 days 30 mg/l is as lethal as 100 mg/l for coral recruits of Pocillopora damicornis Survivorship (%) 100 80 60 40 20 0 0 5 10 25 30 Time (days) 15 20
12. 10 larvae 559 recruits Sediments collected in Orpheus and sieved ˂63 µm Incubation: 24 h Sedimentation: 1h approximately 4 enrichment levels Sample times: 3, 6, 12, 24, 48 h 5 vials Experiment 2: Effects of organically enriched sedimentation on recruit survivorship Survivorship: % recruits alive at each sample time and after 7 days of exposure Water sample analysis: Nitrogen, Phosphorus, Carbon, Pigments, Bacterial community (454 sequencing) Sediments Recruits 125 vials Control 0.1 OC% 0.3 OC% 0.9 OC%
13. Experiment 2: Effects of organically enriched sedimentation on recruit survivorship Time x enrichment interaction not significant p<0.05 p<0.05 Enriched sediments can damage recruits of P. damicornis in less than 2 days Survivorship Exposure time (hours) Enrichment (OC%)
14. Experiment 2: Effects of organically enriched sedimentation on recruit survivorship Enriched sediments have long-term impacts on recruits of P. damicornis even when removed after a couple of hours Survivorship 7 days after exposure p<0.05 Exposure time (hours)
15. Conclusions ü Survivorship of coral recruits and ultimately their abundance and distribution are negatively impacted by: - suspended sediments - organically enriched sediments ü Benthic habitats exposed to excessive turbidity due to river run- off may be sub-optimal for corals.
16. Questions and suggestions are appreciated Thanks!